JP5226292B2 - Tandem time-of-flight mass spectrometry - Google Patents

Description

  The present invention relates to a tandem time-of-flight mass spectrometry method used in the field of quantitative analysis, qualitative simultaneous analysis of trace compounds, and structural analysis of sample ions.

[Time of Flight Mass Spectrometer (TOFMS)]
TOFMS is a mass spectrometer that determines the mass-to-charge ratio of ions from the time it takes to reach a detector by accelerating and flying ions with a certain amount of energy. In TOFMS, ions are accelerated with _a constant pulse voltage Va. At this time, the ion velocity v is calculated from the energy conservation law.
_{^{mv 2/2 = qeV a .........}} (1)
v = √ (2qeV / m) (2)
Where m: ion mass, q: ion charge, e: elementary charge.

  A detector placed after a certain distance L arrives at a flight time T.

T = L / v = L√ (m / 2qeV) (3)
TOFMS is a device that separates masses by using the fact that the time of flight T varies depending on the mass m of ions according to equation (3). FIG. 1 shows an example of a linear TOFMS. Reflective TOFMS is also widely used, which can improve energy convergence and extend flight distance by placing a reflection field between the ion source and the detector. FIG. 2 shows an example of a reflective TOFMS.

[Helix orbit TOFMS]
The mass resolution of TOFMS is T, where total flight time is T and peak width is ΔT.
Mass resolution = T / 2ΔT (4)
Defined by That is, if the peak width ΔT is kept constant and the total flight time T can be extended, the mass resolution can be improved. However, in the conventional linear and reflective TOFMS, extending the total flight time T, that is, extending the total flight distance directly leads to an increase in the size of the apparatus. A multi-circular TOFMS (Non-Patent Document 1) is an apparatus developed to avoid an increase in the size of the apparatus and achieve high mass resolution. This apparatus can extend the total flight time T by using four toroidal electric fields combining a Mazda plate with a cylindrical electric field and by making multiple rounds of an 8-shaped orbit. In this apparatus, the spatial extent and temporal extent on the detection surface due to the initial position, initial angle, and initial kinetic energy are successfully converged to the first order term.

  However, TOFMS that makes multiple rounds of closed orbits has the problem of “overtaking”. This occurs because light ions (high speed) overtake heavy ions (low speed) because they orbit around the closed orbit. For this reason, the basic concept of TOFMS, which arrives in order from light ions to the detection surface, does not work.

  The helical orbital TOFMS was devised to solve this problem. The helical trajectory type TOFMS is characterized by shifting the start and end points of the closed orbit in the direction perpendicular to the closed orbit plane. In order to realize this, a method in which ions are incident obliquely from the beginning (Patent Document 1), a method in which the start point and end point of a closed orbit are shifted in a vertical direction using a deflector (Patent Document 2), and a laminated toroidal electric field are There is a method used (Patent Document 3).

  As a similar concept, a TOFMS in which the trajectory of a multiple reflection type TOFMS (Patent Document 4) in which overtaking occurs is made into a zigzag type has also been devised (Patent Document 5).

[MALDI method and delayed extraction method]
The MALDI method is a method in which a sample is mixed and dissolved in a matrix (liquid, crystalline compound, metal powder, etc.) that has an absorption band at the wavelength of the laser light to be used, and then the sample is vaporized or ionized by laser irradiation. is there. In ionization with a laser represented by the MALDI method, a delayed extraction method is used in most cases because the initial energy distribution at the time of ion generation is large and this is converged in time. This is a method in which a pulsar voltage is applied with a delay of several hundred nsec from laser irradiation.

  A conceptual diagram of a general MALDI ion source and delayed extraction method is shown in FIG. A sample obtained by mixing and dissolving a sample in a matrix (liquid, crystalline compound, metal powder, etc.) is placed on the sample plate. A lens 2, a mirror 2, and a CCD camera are arranged so that the state of the sample can be observed. A sample is irradiated with a laser by a lens 1 and a mirror 1 to vaporize or ionize the sample. The generated ions are accelerated by the voltage applied to the intermediate electrode 1 and the base electrode and introduced into the mass spectrometer.

  Next, the sequence of time-of-flight measurement using the delay extraction method is shown in FIG. First, the potential of the intermediate electrode 1 and the sample plate are set to the same potential Vs. Next, after receiving a signal from the laser to inform the laser oscillation, the potential Vs of the intermediate electrode 1 is changed to the potential V1 at high speed after several hundred nsec, and a potential gradient is created between the sample plate and the intermediate electrode 1 Accelerate ions. The start time of flight time measurement is synchronized with the rise time of the pulsar.

[Vertical acceleration TOFMS]
Since the MALDI method generates ions in a pulsed manner, it is very compatible with TOFMS. However, there are many ionization methods for mass spectrometry such as electron impact (EI), chemical ionization (CI), electrospray (ESI), and atmospheric pressure chemical ionization (APCI). Orthogonal Acceleration (vertical acceleration method) was developed to combine these ionization methods with TOFMS.

  FIG. 4 shows a conceptual diagram of TOFMS using the vertical acceleration method (hereinafter, referred to as vertical acceleration type TOFMS). An ion beam generated from an ion source that continuously generates ions is continuously transported to the vertical acceleration unit with a kinetic energy of several tens of eV. In the vertical acceleration section, a pulse voltage of about 10 kV is applied to accelerate ions in a direction perpendicular to the transport direction from the ion source. After the pulse voltage is applied, the time until the ions reach the detector varies depending on the mass of the ions, so that mass separation is performed.

[MS / MS measurement and TOF / TOF equipment]
In general mass spectrometry, ions generated by an ion source are separated and detected for each m / z value by a mass analyzer. The result is expressed in the form of a mass spectrum in which the m / z value and relative intensity of each ion are graphed, and the information obtained at this time is only the mass. Hereinafter, this measurement is referred to as MS measurement with respect to the MS / MS measurement described later. On the other hand, specific ions generated in the ion source are selected by the first-stage MS device (the selected ions are called precursor ions), and the ions are spontaneously or forcibly cleaved, and the generated ions (cleavage) The generated ions are called product ions). MS / MS measurement is performed by mass analysis using a subsequent MS apparatus. An apparatus capable of this is called an MS / MS apparatus.

  In the MS / MS measurement, the m / z value of the precursor ion, the m / z value of the product ion generated by a plurality of cleavage paths, and the relative intensity information are obtained, so that the structure information of the precursor ion can be obtained (FIG. 5). ). An MS / MS system in which two TOFMSs are connected in series is generally called TOF / TOF, and is mainly used in systems that employ a MALDI ion source. As shown in FIG. 6, a conventional TOF / TOF is composed of a linear TOFMS and a reflective TOFMS. In the meantime, an ion gate for selecting a precursor ion is provided, and a convergence point of the first TOFMS is arranged in the vicinity of the ion gate.

The precursor ion is forcibly cleaved when it is spontaneously cleaved or in a collision chamber arranged before the reflection field of the first TOFMS or the second TOFMS. The kinetic energy of the cleavage product ions is distributed in proportion to the mass of the product,
U _p = U _i × m / M (5)
Where U _{p is} the kinetic energy of the product ion, U _{i is} the kinetic energy of the precursor ion, m is the mass of the product ion, and M is the mass of the precursor ion. In the second TOFMS including the reflection field, the time of flight varies depending on the mass and kinetic energy, so that the product ion can be subjected to mass analysis.

M. Toyoda, D. Okumura, M. Ishihara and I. Katakuse, J. Mass Spectrom., 2003, 38, pp. 1125-1142. JP 2000-243345 A JP 2003-86129 A JP 2006-12782 A British Patent No. 2080021 International Publication No. 2005/001878 Pamphlet JP 2005-302728 A U.S. Pat. No. 6,441,369 US Pat. No. 6,300,567 U.S. Pat. No. 4,625,112 JP 2006-196216 A

[Problems of conventional technology]
Generally, in sample ions, isotopes are present in carbon, oxygen, nitrogen, hydrogen, and the like constituting the sample ions, so that there are multiple types of sample ion masses depending on the combination. A group of peaks of the same molecule that appear in the mass spectrum but different in mass is generally referred to as an “isotope peak”. An example of Angiotensin I (C ₆₂ H ₉₀ N ₁₇ O ₁₄ ) is shown in FIG. From FIG. 7, it can be seen that some ions exist at intervals of 1 unit (unit is a mass unit in which the mass of ¹² C is defined as ¹² units). A peak having the smallest mass, that is, only a single isotope such as ¹² C, ¹⁶ O, ¹⁴ N, ¹ H, etc. is called a “monoisotopic ion”.

  Now, when the linear TOFMS is adopted as the first TOFMS as in the prior art, the flight distance can only be about several hundred mm. At such a flight distance, the flight time difference between the isotope peaks is less than 10 nsec, and considering the switching speed of the ion gate, it is impossible to achieve high selectivity, and a plurality of isotope ions are allowed to pass. It will be. However, selecting a plurality of isotope ions presents a major problem. This will be described below.

  If the second TOFMS including the reflected electric field is a system that fully satisfies energy convergence (a system in which the flight time does not change due to the difference in kinetic energy of product ions), the time to pass through the first TOFMS depends on the mass of the precursor ion, and the second TOFMS The flight time of is dependent on the mass of product ions.

  To simplify the discussion here, consider the case where a monovalent precursor ion is cleaved into a monovalent charged product ion having two isotopes and neutral particles (see Tables 1 and 2).

Before the cleavage, product ions and neutral particles were bonded, so there are 16 combinations of precursor ions (Table 3), but there are 7 masses (M, M + 1, M + 2, M + 3, M + 4, M + 5, M + 6). : However, M = m + n). The arrival time of each cleavage species to the detector is defined as follows. The flight time of the precursor ion of mass X in the first TOFMS is T1 _{, X} , and the flight time of the product ion of mass Y in the second TOFMS is T2 _{, Y.} (T1 _{, X} + T2 _{, Y} ).

The intensity ratio is expressed by multiplying the intensity ratio of the product ion and neutral particles in each case. For _{simplicity, R m: R m + 1} : R m + 2: R m + 3 = R n: R n + 1: R n + 2: R n + 3 = 0.4: 0.3: 0. Assuming 2: 0.1, the intensity ratio of each combination and the isotope peak ratio of the precursor ion are as shown in Table 3.

  Looking at Table 3 from the product ion perspective, it looks like Table 4.

The product ion spectrum near the mass m is as shown in FIG. Where ΔT ₁ is the time difference between the isotope peaks of the precursor ions in the first TOFMS, and ΔT ₂ is the time difference between the isotope ions of the product ions in the second TOFMS. The time difference of flight between each isotope is considered to be almost the same.

  As shown in FIG. 8, since the masses of the precursor ions are different, the time of flight between product ions (for example, 1, 2, 4, 7) having the same mass is shifted. Actually, since the peak has a width, the peak 2 may be the base of the peak 1 or the base line between the peak 1 and the peak 3 may rise. Either way, high mass accuracy of product ions cannot be obtained.

  One effective method for solving this problem is to select only the precursor monoisotopic ion. When a monoisotopic ion is selected as the precursor ion, the only ions that can be cleaved from it are the monoisotopic ions, eliminating the effects of isotope peaks, simplifying the interpretation of spectra, and improving mass accuracy. it can.

  Since the helical trajectory TOFMS has time and space convergence for each round, an intermediate convergence point is once created in the trajectory of the spiral trajectory TOFMS in both cases of the MALDI method and the vertical acceleration method. The distance is less than or equal to the distance to the intermediate convergence point in the case of linear TOFMS. Like the delay time of the MALDI method, the factors affecting the time convergence at the intermediate convergence point derived from the ion source are Less than the same level.

  Furthermore, since the helical trajectory type TOFMS can maintain the state at the intermediate convergence point even if the number of laps increases, the flight distance of the first TOFMS can be increased by about 50 to 100 times while maintaining the time convergence. That is, the time-of-flight difference between isotope ions of the precursor ion can be increased by about 50 to 100 times, and only one isotope ion can be selected.

  However, as the mass of the precursor ion increases, the proportion of monoisotopic ions in the total isotope ions decreases. Therefore, in the case of ions having a large mass, there is a problem that the sensitivity of product ions is deteriorated when the above-described method is employed. Depending on the type of sample, the presence ratio of precursor ions and isotope ions of product ions may have an important meaning for structure determination. However, if only monoisotopic ions are selected as precursor ions, There is a problem that abundance information of isotope ions in ions is lost.

  An object of the present invention is to propose a method for solving the above problems in view of the above-mentioned points. By adopting helical TOFMS as the first TOFMS, it is possible to select each isotope ion by ion gate and perform MS / MS measurement. However, when the main isotope ions are selected as the precursor ions, the time of flight of the first TOFMS of each isotope ion is different if the acceleration voltage and sector electric field voltage are set under the same conditions. Such a problem arises that the spectrum analysis becomes complicated.

  Therefore, when obtaining product ions using the main isotope ions as precursor ions, the acceleration voltage and the electric sector voltage are varied to adjust the flight time of the first TOFMS to be the same. Since the second TOFMS has a wide kinetic energy convergence, it can absorb a slight difference in kinetic energy due to this adjustment. Further, since the second TOFMS has a wide kinetic energy convergence, product ions having the same m / z value but different kinetic energies arrive at the detector at the same time. Therefore, the mass spectra can be added together.

  As a result, when only a monoisotopic ion is selected as a precursor ion, the sensitivity decreases in the case of an ion with a large mass, and the abundance information of the isotope ion in the product ion is lost. Can do.

In order to achieve this object, a tandem time-of-flight mass spectrometry method according to the present invention includes:
An ion source for ionizing the sample;
Accelerating means for accelerating the generated ions in a pulsed manner;
A first time-of-flight mass spectrometer configured with a time-of-flight ion optical system and flying accelerated ions;
An ion gate that selects only ions having a predetermined mass-to-charge ratio from ions mass-separated by the first time-of-flight mass spectrometer;
A second time-of-flight mass spectrometer that is disposed downstream of the ion gate and analyzes the mass of cleaved ions;
In the mass spectrometry of the tandem time-of-flight mass spectrometer, comprising a detector that detects ions that have passed through the second time-of-flight mass spectrometer.
When the plurality of isotope ions of the ions are selected one by one by the ion gate and cleaved to measure the product ions, the first time-of-flight mass spectrometer is measured in the same flight time. The acceleration voltage of the first time-of-flight mass spectrometer and / or the set voltage of the time-of-flight ion optical system are finely adjusted so that the time of flight can be passed. Nevertheless, the first step of acquiring each product ion spectrum so as to have the same time,
A second step of synthesizing the entire product ion spectrum by superimposing and adding the acquired product ion spectra derived from each isotope ion at the same time of flight;
A third step of converting the time-of-flight axis of the synthesized product ion spectrum into a mass axis is provided.

  Further, the ion source is a MALDI ion source.

  Further, the ion source is a continuous ion source, the acceleration means is a vertical acceleration section, and both are connected via an ion transport means.

  In the second step, the peak intensity ratio of uncleaved ions in each product ion spectrum is the same as the peak intensity ratio of each isotope ion when mass-separated in the first time-of-flight mass spectrometer. Thus, after multiplying each product ion spectrum by a predetermined coefficient, the entire product ion spectrum is synthesized.

  Further, the first time-of-flight mass spectrometer is a multi-turn type time-of-flight mass spectrometer composed of a plurality of sector electric fields.

  In addition, the first time-of-flight mass spectrometer is a spiral orbit type time-of-flight mass spectrometer composed of a plurality of sector electric fields.

According to the tandem time-of-flight mass spectrometry of the present invention,
An ion source for ionizing the sample;
Accelerating means for accelerating the generated ions in a pulsed manner;
A first time-of-flight mass spectrometer configured with a time-of-flight ion optical system and flying accelerated ions;
An ion gate that selects only ions having a predetermined mass-to-charge ratio from ions mass-separated by the first time-of-flight mass spectrometer;
A second time-of-flight mass spectrometer that is disposed downstream of the ion gate and analyzes the mass of cleaved ions;
In the mass spectrometry of the tandem time-of-flight mass spectrometer, comprising a detector that detects ions that have passed through the second time-of-flight mass spectrometer.
When the plurality of isotope ions of the ions are selected one by one by the ion gate and cleaved to measure the product ions, the first time-of-flight mass spectrometer is measured in the same flight time. The acceleration voltage of the first time-of-flight mass spectrometer and / or the set voltage of the time-of-flight ion optical system are finely adjusted so that the time of flight can be passed. Nevertheless, the first step of acquiring each product ion spectrum so as to have the same time,
A second step of synthesizing the entire product ion spectrum by superimposing and adding the acquired product ion spectra derived from each isotope ion at the same time of flight;
Since the third step of converting the time-of-flight axis of the synthesized product ion spectrum into the mass axis is provided,
It has become possible to provide a new tandem time-of-flight mass spectrometry that has overcome the shortcomings of conventional tandem time-of-flight mass spectrometry.

  Embodiments of the present invention will be described below with reference to the drawings. In the description of the present embodiment, an example in which the spiral orbit TOFMS composed of four electric sector electric fields is used as the first TOF will be described. I can say that.

[Example 1]
FIG. 9 is a diagram showing a first embodiment according to the present invention. (A) is the figure which looked at the apparatus to the Z direction, (b) is the figure seen from the arrow direction (Y direction) of (a) figure. In the figure, 11 is a MALDI ion source, 12 is a deflector that deflects the precursor ions generated by the MALDI ion source 11 toward the subsequent electric field, and 13 to 16 are multilayered in the Z direction to form an 8-shaped spiral trajectory. 18 is a first detector that detects a precursor ion, 18 is an ion gate that selects a precursor ion, 19 is a collision chamber that cleaves the precursor ion, and 20 is an ion that has passed through the collision chamber 19. Is a reflected field 21, and 21 is a second detector for detecting ions reflected by the reflected field 19.

  The operation of the apparatus configured as described above will be described as follows. First, the sample compound group is ionized by the MALDI ion source 11, and the ions are accelerated by a pulse voltage. Ions emitted from the MALDI ion source 11 are adjusted in the angle of the flight trajectory by the deflector 12 and enter the sector electric fields 13 to 16.

  The ions sequentially pass through the first sector electric field 13, the second sector electric field 14, the third sector electric field 15, and the fourth sector electric field 16, and make one round. At this time, since the position in the Z direction is deviated from the previous round, it moves in the Z direction while repeating the rounds.

  In the case of MS measurement, ions are detected using the first detector 17 arranged on the orbit. In the case of MS / MS measurement, the first detector 17 is removed from the ion trajectory, and the ions are caused to travel straight toward the ion gate 18.

  When the ion gate voltage is OFF, ions can pass through the ion gate 18 and cannot pass when the ion gate voltage is ON. Therefore, the ion gate voltage is turned off only during the time when the precursor ion to be selected passes through from the ion group that has completed the last round, and the isotope peak having the precursor ion is selected.

  The selected precursor ion enters the collision chamber 19 and is cleaved by collision with the collision gas in the collision chamber. Precursor ions that have not been cleaved and product ions that have been cleaved pass through the reflected field 20 and are detected by the second detector 21. Since the time for turning back the reflection field 20 varies depending on the mass of the precursor ion, mass analysis can be performed on the precursor ion, the precursor ion, and the product ion for each cleavage path.

The above operation is performed by individually selecting the main isotope ions of the precursor ions. At this time, for example, assuming that the masses of main isotope ions are M = 1000, M + 1 = 1001, and M + 2 = 1002, when the acceleration voltage is constant, the time of flight T _{1, M} , T of the _first TOFMS of each isotope ion _{1, M + 1} and T1 _{, M + 2} are calculated from the equation (3), T1 _{, M + 1} = √ (1001 × T1 _{, M} / 1000)
T1 _{, M + 2} = √ (1002 × T1 _{, M} / 1000)
And slightly different. In order to achieve the object of the present invention, in order to satisfy T1 _{, M} = T1 _{, M + 1} = T1 _{, M + 2} , acceleration of ions of masses M + 1 and M + 2 according to equation (3). The voltage (fan electric field voltage if necessary) may be set to 1001/1000 times for mass M + 1 ions and 1002/1000 times for mass M + 2 ions.

  When such an operation is performed, the difference in kinetic energy for each isotope ion changes by 0.1% and 0.2% when M is 1000. As the mass M increases, the difference value becomes relatively smaller.

  The amount of change in kinetic energy is much smaller than the difference in kinetic energy due to cleavage described in Equation (4), and the ion of the second TOFMS can converge the change in kinetic energy due to cleavage as an ion optical system. If so, there is no effect. Therefore, if the product ion spectra are added together while matching the isotope peaks of each precursor ion in time of flight, the interpretation is not complicated and the sensitivity is high. Can also be obtained.

[Example 2]
FIG. 10 is a diagram showing a second embodiment according to the present invention. The configuration of the present embodiment is the same as that of FIG. In Example 1, the acceleration voltage is switched for each isotope ion. However, depending on the case, it may be difficult to set an appropriate acceleration voltage for each isotope ion. In such a case, MS / MS measurement is first performed for monoisotopic ions, and for other isotope ions, the acceleration voltage is scanned before and after the set acceleration voltage to perform MS / MS measurement. Based on the flight time T _{2, M} of the monoisotopic ion, T _{2, M + 1} and T _{2, M + 2} can be predicted, and if the acceleration voltage is set appropriately _, T _{1, M} = Since T1 _{, M + 1} = T1 _{, M + 2} , the total flight time T1 _{, X} + T2 _{, X} (X = M + 1, M + 2) of the precursor ions that were not cleaved from each isotope ion , ……) can be expected. Of the product ion spectra obtained by scanning, the precursor ions that have not been cleaved are selected within the allowable error range from the expected flight time, and added together to synthesize the product ion spectrum.

[Example 3]
The configuration and operation of the present embodiment are almost the same as those of the first and second embodiments, and only the operation during the synthesis of the product ion spectrum is different. That is, since the synthesis of the product ion spectrum is performed by acquiring a plurality of spectra, there is a possibility that the intensity differs in each spectrum. Therefore, when synthesis is performed, an appropriate coefficient is applied to the intensity axis of the mass spectrum so that the peak intensity ratio of each precursor ion observed by the second TOFMS matches the isotope ratio of the precursor ion.

[Example 4]
FIG. 11 is a diagram showing a fourth embodiment according to the present invention. (A) is the figure which looked at the apparatus to the Z direction, (b) is the figure seen from the arrow direction (Y direction) of (a) figure. In the figure, 31 is an ion source, 32 is an ion transport part such as an ion guide for transporting a precursor ion generated by the ion source 31, and 33 is a vertical acceleration for accelerating the precursor ion transported from the ion transport part 32 in the vertical direction. And 34 are deflectors for deflecting the precursor ions accelerated by the vertical accelerating unit toward the subsequent sector electric field, and deflectors for adjusting the incident angle to the subsequent sector electric field, and 35 to 38 are multilayered in the Z direction. A sectoral electric field that forms a helical orbital ion optical system, 39 is a first detector that detects precursor ions, 40 is an ion gate that selects precursor ions, 41 is a collision chamber that cleaves precursor ions, and 42 is a collision chamber. Reference numeral 43 denotes a reflection field in which ions that have passed through 41 are incident, and reference numeral 43 denotes a second detector that detects ions reflected by the reflection field 41.

  This embodiment is different from Embodiments 1 to 3 in that a continuous ion source is connected by applying the vertical acceleration method instead of the MALDI ion source, and the other points are the same as those in Embodiments 1 to 3. It is.

  It can be widely used for tandem measurement of time-of-flight mass spectrometers.

It is a figure which shows an example of the conventional linear TOFMS apparatus. It is a figure which shows an example of the conventional reflection type TOFMS apparatus. It is a figure which shows an example of the conventional MALDI ion source. It is a figure which shows an example of the conventional vertical acceleration type TOFMS apparatus. It is a conceptual diagram of the conventional MS / MS measurement. It is a figure which shows an example of the conventional TOF / TOF apparatus. It is a figure which shows the isotopic peak and monoisotopic peak of angiotensin I. FIG. 5 is a conceptual diagram of MS / MS measurement in which a plurality of precursor ions are selected. It is a figure which shows one Example of the TOF / TOF apparatus concerning this invention. It is a figure which shows one Example of the TOF / TOF measuring method concerning this invention. It is a figure which shows another Example of the TOF / TOF apparatus concerning this invention.

Explanation of symbols

11: MALDI ion source, 12: deflector, 13: first sector electric field, 14: second sector electric field, 15: third sector electric field, 16: fourth sector electric field, 17: first detector, 18 : Ion gate, 19: collision chamber, 20: reflection field, 21: second detector, 31: ion source, 32: ion transport part, 33: vertical acceleration part, 34: deflector, 35: first sector electric field, 36: second sector electric field, 37: third sector electric field, 38: fourth sector electric field, 39: first detector, 40: ion gate, 41: collision chamber, 42: reflection field, 43: second Detector

Claims (6)

An ion source for ionizing the sample;
Accelerating means for accelerating the generated ions in a pulsed manner;
A first time-of-flight mass spectrometer configured with a time-of-flight ion optical system and flying accelerated ions;
An ion gate that selects only ions having a predetermined mass-to-charge ratio from ions mass-separated by the first time-of-flight mass spectrometer;
A second time-of-flight mass spectrometer that is disposed downstream of the ion gate and analyzes the mass of cleaved ions;
In the mass spectrometry of the tandem time-of-flight mass spectrometer, comprising a detector that detects ions that have passed through the second time-of-flight mass spectrometer.
When the plurality of isotope ions of the ions are selected one by one by the ion gate and cleaved to measure the product ions, the first time-of-flight mass spectrometer is measured in the same flight time. The acceleration voltage of the first time-of-flight mass spectrometer and / or the set voltage of the time-of-flight ion optical system are finely adjusted so that the time of flight can be passed. Nevertheless, the first step of acquiring each product ion spectrum so as to have the same time,
A second step of synthesizing the entire product ion spectrum by superimposing and adding the acquired product ion spectra derived from each isotope ion at the same time of flight;
A tandem time-of-flight mass spectrometry method comprising a third step of converting a time-of-flight axis of a synthesized product ion spectrum into a mass axis. The tandem time-of-flight mass spectrometry method according to claim 1, wherein the ion source is a MALDI ion source. The tandem time-of-flight mass spectrometry method according to claim 1, wherein the ion source is a continuous ion source, the acceleration means is a vertical acceleration unit, and both are connected via an ion transport means. In the second step, the peak intensity ratio of uncleaved ions in each product ion spectrum is made to coincide with the peak intensity ratio of each isotope ion when mass-separated in the first time-of-flight mass spectrometer. 2. The tandem time-of-flight mass spectrometry method according to claim 1, wherein the entire product ion spectrum is synthesized after multiplying each product ion spectrum by a predetermined coefficient. The tandem time-of-flight mass spectrometer according to claim 1, wherein the first time-of-flight mass spectrometer is a multi-turn type time-of-flight mass spectrometer composed of a plurality of electric sector fields. The tandem time-of-flight mass spectrometer according to claim 1, wherein the first time-of-flight mass spectrometer is a spiral orbit type time-of-flight mass spectrometer composed of a plurality of electric sector fields.

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